Chemical modifications of the molecular structure of tetrodotoxin which may retain the sodium channel blocking activity of tetrodotoxin are being investigated. These studies will be aimed primarily at modification at the primary hydroxyl function at C-11 (oxidation to aldehyde and acid with formation of suitable derivatives), and periodate oxidation at C-11, C-6 to form 11-nor-6-tetrodotoxinone. The formation of various derivatives of this ketone (cyano-hydrin, oxime, hydrozones, etc.) will be studied.